Vehicle brake



Dec. 22, 1931.

A. P. WARNER ET AL VEHICLE BRAKE Filed Jan. 10, 1928 4 Sheets-Sheet Dec.22, 1931. A. P. WARNER ET AL Filed Jan. 10, 1928 7/6 mam Dec. 22, 1931.A. P. WARNER ET AL 1,837,384

VEHICLE BRAKE Filed Jan. 10, 1928 4 Sheets-Sheet I5 Dec. 22, 1931. A. P.WARNER :1- AL VEHICLE BRAKE Filed Jan. 10, 1928 4 Sheets-Sheet 4 aim SEE

JiTth/wr P ZUcLrIZ//Z' Jiddz) 5. Cadm/am/ 4 W M Patented Dec. 22', 1931UNITED STATES .PA'TI'ENT OFFICE ARTHUR 1. WARNER AND ADDI BENJAMINCADMAN, OF IBELOIT, WISCONSIN, AS-

SIGN ORS T0 WARNER ELECTRIC BRAKE CORPORATION, OF SOUTH BELOIT,ILLINOIS,

A CORPORATION OF ILLINOIS VEHICLE BRAKE Continuation of applicationSerial No. 156,355, filed December 22, 1926. This 10, 1928, Serial No.245,714.

The brakes commonly provided on present day automobiles, trucks and thelike have certain well known deficiencies and disadvantages, a briefstatement of which will be conducive to a better understanding of ourinvention.

'First, these present brakes'are operated by.

the physical effort of the driver, which necessitates the use of brakingsurfaces or linings having the highest possible coeflicient of frictionin order to obtain sulficient braking force. The best lining known forthis purpose is a fabric material which is relatively soft and thereforewears rapidly, necessitating repeated renewal during the life of thevehicle. Brakes constructed according to our invention do not dependupon the physical effort of the driver but utilize the momentum of thevehicle as a source of power which will effect a very powerful brakingpressure and for this reason we are able to use braking surfaces orlinings such as metal or hard friction material having a much lowercoefficient of friction but giving vastly greater wear andlonger lifethan the present brake linings.

Second, brakes now in use are operated from the foot pedal byconnections usually in the form of links, levers, and rock shafts whichadd tothe cost of the brakingmechanism and which are affected by wear,looseness, springing of the parts, expansion of the brake drums byheating, etc. to such an extent that the braking action variesmaterially and the braking force on the different wheels is unbalanced,thereby requiring frequent adjustment especially with four-wheel brakeson automobiles where the front wheels are mounted on pivoted steeringknuckles. Our brake eliminates the necessity for such mechanicalconnections, is unaffected by distortion of the brake drum, andtherefore results in a more perfect balance of the brak- REISSUEDapplication filed January wheels without corrected by hydraulic brakesbut the benefits are, to a large extent, offset by disadvantagesincident to the leaking of the liquid, clogging of the ports, etc. havebeen used on larger types of vehicles but are objectionable because oftheir hi h cost of installation and maintenance and t e difficulty ofinstantaneously and accurately controlling them. Our electric brakecorrects the difficulties outlined and at the same time avoids theofl'setting disadvantages of hydraulic and air brakes.

It is a general object of our invention to provide a vehicle brake whichis superior to any brake now known and. which has four outstandingamount of physical effort by the driver, (6) one that will produce anextremely powerful braking force, (a) one that is extremely sensitive,positive and uniform in controllability by the driver, and (d) one whichis simple and durable in construction, inexpensive to manufacture, lowin maintenance cost, and is not subject to the necessity of frequent adjustment to maintain its efliciency.

In carrying out this general object we have devised a vehicle brakewhich includes the braking means proper- (herein shown in the form of adrum and a coacting braking device), and a pair of magnetic friction elements electrically controlled by the driver through suitable means suchas a rheostat, said elements deriving power from the motion of thevehicle and being arranged to operate said braking means throughconnections so constructed as to multiply the force received from saidfriction elements and deliver the increased force to said braking means.

Another object is to provide a novel vehicle brake wherein the brakingforce is derived through the frictional gripping engagement of magneticelements which are so constructed that they are operable from the usualstorage battery or other source of electrical energy without undulydischarging or advantageous characteristics, -v1z., (a) a brake thatrequires a negligible Air brakes also overloading the same under normalconditions of braking.

Still another object is to provide a novel operator in a vehicle brakecapable of deriving variable actuating forces from the momentum of thevehicle, including an electromagnetically controlled friction devicethe.

coacting elements of which are so related that a sensitive operation ofthe device and consequently a graduated braking action is obtainedthroughout the entire range of variation of the energizing current inthe device.

A further object is to provide, in a brake I mechanism wherein thebraking action is govtrically controlled brake operator of the momentumtype which is individual to and compactly associated with a brake of theusual drum type on a vehicle wheel, such associationbeing accomplishedbyso positioning the magnetic friction elements and force augmentingconnections constituting the operator Within or in such close proximityto the space normally provided for the brake structure on said wheel asto avoid interference between the parts of the operator and the wheel,the axle or other parts of the vehicle.

A further object is to provide an electromagnetically controlled brakeof the momentum type for a dirigible wheel wherein the associated partsof the electromagnetic operator and the braking members are arranged ina compact unit which is operatively disposed about a free open axialspace of sufficient dimensions to accommodate the usual yoke typesteering knuckle construction without disturbing the normal relationbetween the plane of rotation of the wheel and the pivotal axis of theknuckle, and without material increase in the dimensions of the brakestructure relative to the diameter of the wheel.

Another object is to provide an electricallycontrolled momentum brakefor vehicles which will respond instantly and uniformly to theapplication of current thereto and produce a brakin action determinedsolely by the strength of said current, and which has means foreffectually restoring its operating parts to normal position after thecurrent flow has been cut oif so as to quickly and reliably release thebrake.

It is also an object of this invention to provide a novel electricallycontrolled operator for a vehicle brake of the momentum type which isoperable to set the brake in a small fraction of one revolution of thewheel following the energization of the electric control means.

Other objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings, in which:

Figure l is a fragmentary View in vertical section of a vehicle wheelequipped with an electric brake embodying the features of the presentinvention.

Figs. 2 and 3 are sectional views taken respectively along the lines 22and 33 of Fig. 1.

Fig. 4 is an enlarged sectional view on the line 4-4 of Fig. 2.

Fig. 5 is a diagrammatic View of the electrical control circuit for thebrake.

Fig. 6 is a view in vertical section of a dirigible vehicle wheelsupporting a pivoted axle and equipped with an electric brake embodyingthe present invention, as seen on the plane of the line 66 in Fig. 7.

Fig. 7 is a side elevation of the brake structure shown in Fig. 6 with aportion of the structure housing broken away to disclose the internalconstruction, as viewed on the planes of the line 77 in Fig. 6.

Fig. 8 is a fractionalv detailed view in section taken on the plane ofthe line 8-8 of Fig. 6.

Although the invention is susceptible of various modifications andalternative constructions, we have shown and herein described in detailthe preferred embodiment but it is to be understood that we do notthereby intend to limit the invention to the specific form disclosed butintend to cover all modifications and alternative constructions fallingwithin the spirit and scope of the invention as expressed in theappended claims.

Generally stated, the present invention includes friction braking means,preferably of the shoe or band type, and a magnetic friction operatortherefor controllable by the vehicle driver by regulating the flow ofcurrent thereto from a storage battery or other source of electricenergy on the vehicle to be braked, the operator bein adapted whenenergized to derive energy from the motion or momentum of the vehicleand to apply this energy to said braking means with increased mechanicaladvantage. The operator, inthe embodiments selected for the purpose ofillustration, is individual to the brake on one vehicle wheel andincludes a friction device composed of two magnetic friction elements,one rotatable with the vehiclewheel, the other being operativelyconnected to the braking means through a force-augmenting mechanism forsetting the brake upon limited oscillation of the driven element ineither direction from its brake-released position in which it isnormally maintained. An electromagnetic winding forms, with one of saidis carried along therewith for a'short angular distance, therebyactuating the force-multiplying mechanism to operate the braking means.When the brake becomes set, the unity of motion of the elements isbroken and the resulting frictional slippage between the elements allowsfor further rotation of the' driving element which holds the driven ele-1 ment in brake-setting position so long as the elements remainmagnetized, but upon the interruption of the energizing current theparts of the operator are quickly restored to brake-released position.This may take place after the vehicle has come to rest or its speedreduced to the extent desired by the driver. To describe the exemplaryform of the in 'vention more particularly reference will first be madeto Figs. 1 to 5 of the drawings wherein a drum brake of the internallyexpansible type is illustrated in conjunction with a standard vehiclewheel mounted on the end of a dead or stationary axle 6, the size andshape of which is determined by. the-Weight and type of the vehicle onwhich .the axle is employed. Herein the wheel is shown as comprisingspokes 7 secured between flanges 8 of a hub 9 which is rotatably mountedin the conventional way through bearings on the end or spindle 10 of theaxle. 'A nut 11 threaded onto the spindle serves to holdthe wheel theposition on the axle. This type of wheel and the bearing therefor, thusselected to illustrate the present brake, are commonly employed on heavyduty vehicles such as trucks having dead rear axles and trailers, butthe brake may be equally well adapted for use on wheels monnted'ondriving axles, or on pivoted steering knuckles such as are more commonlyemployed on passenger vehicles.

- Such adaptation to passenger vehicle wheels is shown in Figs. 6 to 8,fully described hereinafter, wherein the exemplary form of the inventionis-associated' with a wheel mounted on a pivoted steering "knuckleofatypejcommonly used on the dirigible front wheels of automobiles.

Mounted on the inner side of the wheel so as to rotate therewith is a.revoluble member in the form of a drum 12 disposed concentrically withrespect to the axis of the wheel and having a diameter substantiallyless than that of the wheel. Herein the drum has an inturned flange 13at its outer end which is bolted or otherwise secured to the.

inner hub flange 8. If desired, the drum may be lined with a strip 14preferably of metallic materialproviding an internal peripheral brakingsurface. p

In the present instance, the inner or open end of the drum is closed bya substantially flat disk member or casing 15 received on the axle 10adjacent the inner end of the hub 9 and firmly held against rotation asby keying an integral hub portion 16 thereof to the axle. The casing maybe reinforced by radially extending internal ribs 17 joined at theirouter ends by a peripheral flange 18..

The gripping devices or shoes which'constitute the non-rotatable part ofthe brake and which are adapted to engage frictionally with the internalsurface of the lining 14 to effect the braking action, may be of anypreferred construction, the ones illustrated in Fig. 3 being segmentalin form, each comprlsing an arcuate backing portion 19 reinforced by aninternal rib 20. Preferably, a

covering 21. of suitable material is secured to each shoe as by meansofbolts. Because of the enormous braking force available with the presentpower brake, the coverings may be made of metal or other material havinga lower friction coefficient but greater resistance to wear anddeterioration by heat than ordinary fabric brake linings. A coveringmaterial known to the trade as brake block and having substantially thesame friction properties as steel but more resistant to wear has beenfound to give the desired braking actlon. The use of such frictionmaterial positively eliminates the well known annoyance called squeakingwhich is prevalent in brakes having fabric linings. v

The brake shoes are arranged in end to end relation within the drum andfirmly held against rotation, at the same time being freely expansible.To this end, the rib 20 of each shoe is formed intermediate its endswith a radially extending flanged recess 22 which fits over a squaredbushing 23 extending parallel to the drum axis and secured by bolts 24passing through apertured bosses formed on the vertical ribs of thecasing 15.

Associated with the adjacent end portions of the brakeshoes in Fig. 3are suitable expanding devices which, when actuated, are adapted tospread the shoes apart and thus press the coverings 21 into brakingengagement with the lining 1 1. In the present instance, these devicescomprise cam blocks 26 mounted between the ends of the shoes tooscillate on fixed axes whichextend parallel to and are spaced asubstantial distance from the axle 10. To this end, the blocks areformed integral with or otherwise rigidly secured to rockshafts 27 and28 which are j ournaled intermediate their ends in bosses formed atopposite ends of the horizontal casing rib 17. Each block 26 is composedof hardened steel and is of substantially rectangular shape so that uponoscillationin tractile springs 27 anchored to the shoes serve tocontract the shoes within the drum as permitted by the angular positionsof the cam blocks. Since the expanding devices thus provided are offsetor located eccentrically with respect to the axle l0 and near theperiphery of the drum, they are not limited in size, shape or degree ofmotion by the axle and wheel hub or by the usual steering knuckle whenthe brake is applied to a dirigible wheel as in Figs. 6 to 8. Thus, theblocks may be constructed short enough to give the desired expansiveforce on the brake shoes for a small oscillation of the rock shafts andyet long enough to prevent wearing or rounding off at their ends underthe operating conditions normally encountered in service.

That part of the operator which is adapted to convert a portion of theenergy available by virtue of the momentum of the vehicle when in motioninto a form which may be utilized for actuation of the brake expandingdevices comprises two friction elements which may be drawn into firmgripping engagement by the energization of an efiicient electromagnet.One of these elements is arranged to rotate in unison with the wheel towhich the brake is applied and in the form herein illustrated comprisesan external pe-- ripheral flange 29 formed integral with or otherwisesupported by the drum so as to present a plane annular surface whichfaces inwardly from the wheel and is substantially flush with the openend of the drum. Thus, in the present instance, the radial width of thissurface is relatively small and its diameter is slightly larger thanthat of the drum.

The friction surface of the other element is of the same diameter as theflange 29 and preferably is on a substantially rigid ring 30 receivedloosely upon an external bearing surface provided by the flange 18 ofthe casing 15. A floating mounting is thus provided for the ring whichholds the ring firmly in coaxial relation with respect to the brake drumat the same time allowing for oscillation of the ring about the drumaxis. Such mounting also allows for approaching movement of the ring inan axial direction toward the flange 29 to permit of frictionalengagement between its flat surface and the friction surface of theflange 29. The ring is of such narrow radial width and spaced soremotely from the axle 6 that it is relatively light in construction anddoes not preclude the expanding devices or other parts of the brakingmeans proper from being simply constructed and mounted in the usual way.

To exclude dust and dirt from the friction surfaces between the elementsand the bearingsurfacesbetweenthe ring 30 and the casing 15, an annularmember 31 constituting an extention of the casing 15 and carried therebyis formed with a peripheral flange 32 enclosing the ring and overlyingthe flange 29.

Means such as adjusting screws 33 may be provided to hold the ring 30adjacent the flange 29 but preferably not so close as to allow anyportion of the ring to become wedged between the ends of the screws andthe rotatable flange 29 due to the slight lateral wobbling of the flangeduring rotation.

In the preferred form of the invention, the two friction elements areformed of magnetic material and constitute the core and armature of apowerful electromagnet which is capable of producing the necessarygripping action when energized with a comparatively small current suchas can be safely drawn from the ordinary storage battery on a vehiclewithout unduly discharging the same. While either of the elements may beconstructed to constitute the magnetic core, it is preferable that thering 30 serve this purpose because the electrical connections theretomay be made simpler and more reliable. Herein the ring 30 carries awinding or coil 34: comprising an insulated conducting wire woundcontinuously in'a series of annular turns to form a single annulus whichis snugly mounted in an annular groove formed in the ring 30 centrallyof its friction surface. The groove may be closed by a ring 35 ofnon-magnetic material thereby tightly sealing the coil 34 within thering 30. With the magnet thus constructed. the two concentricallyarranged portions of the flat friction surface on the ring constitutepole faces of opposite polarity between which a magnetic flux flowswhenever the winding is energized. The area of the friction face of themagnet and the ring 35 which also presents a friction surface is such as.to properly distribute frictional wear and to provide for the rigidityof the magnet structure when griping the rotating flange or armature.T'o lighten the magnet and still leave an ample path for the flow offlux through the magnetic circuit, the back por tion of the ring30, inthe form illustrated, is cut away at its inner and outer peripheraledges.

In operation, the initial flow of current in the magnet winding producesa flux which flows in a mean path indicated approximately by the dottedline 36 in Fig. 4., thereby causing magnetic attraction to the rotatableflange armature. The force thus produced acts in an axial direction todraw each elemental portion of the magnet ring firmly against the flange29. Such intimate gripping engagement may involve a slight yielding ofportions ofvthe flange 29 or the r ng 30. The frictional force resultingfrom the gripping engagement of the magnetic elements tends to producecontinued movement of the driven element or ring along with the rotatingflange and the magnitude of this force is equal to the product of thenormal pressure or magnetic attraction and the friction coefiicientbetween the coacting surfaces.

coil is energize The present magnet is extremely efficient in itsoperation, that is to say, a maximum attractive force is obtained with aminimum number of ampere turns effecting economy in manufacture and witha minimum. current consumption. For example, with a magnet constructedfor use in a brake for a ten-ton freight-hauling vehicle and having acoil of sixty-three turns, an attractive force of four thousand ounds isexerted when the d with a current of 4.7 5 amperes to give a maximumapplication of the brake. This current consumption may be compared tothe rate of consumption of from 7 to 10 amperes in the averageautomobile lighting system and the rate of consumption in a vehiclestarting motor while running of approximately 100 amperes. For use inthe brakes of lighter passenger cars, each brake magnet can be designedto draw a current of less than one ampere for maximum brake applicationand less than one-half ampere for ordinary braking. Thus, the flow ofcurrent to give maximum braking at all four wheels of such a vehiclewould be approximately four amperes which represents a small part of therecharging capacity of the generator provided on modern self-propelledvehicles and even if drawn frequently from the battery,

same.

would not unduly discharge the Among the factors to which the high etfidescribed, the short length of the flux circuit, and the utilization ofall available flux lines produced by the -mag'netic winding. The twofeatures last named result from the use of a single annular windingimmediately surrounded and substantially enclosed by the metal of thering 30 which is of such thick- 4B ness as to conduct the fluxefiiciently.

An important advantage accrulng from the'u'se of friction elements whichare brought into gripping engagement by a force acting in an axlaldirection is that the operation of the elements and therefore thecontrol of the braking action is not materially affected by expansion ofthe drum by the heat developed in braking the vehicle. In other words,since the coacting friction surfaces are disposed radially-orperpendicular to the drum axis, variation in diameter of the rotating ordriving element by heating does not change the operative relation of theelements. Moreover, such axial engagement does not produce an end thruston the vehicle wheel, because the gripping force originates withininstead of externally of the coacting elements. v

The winding 34 for controlling the operation of the friction operator isintended to be energized from the usual storage battery 37 Fig. 5. andpreferably extends from the grounded battery terminal throu h aconductor 40 comprising the vehicle rame, the axle 10, the casing 15 andthe ring 30 which is electrically connected to one terminal end of theWindmg 34. The other battery terminal is connected-to the rheostat 39which in turn is connected to the other winding terminal through aninsulated conductor including a wire 41 and suitable means to allow foroscillation of the magnetic ring 30, this being accomplished in thepresent instance through the medium of the wiping contactconstruction'shown in Fig. 4. For this purpose, an arcuate strip 42 ofinsulating material is mounted on the back of the ring 30 and carries ametallic contact strip 43 connected to the insulated terminal of thewinding 34. Mounted on the closure member 31 is a junction box'44 ofinsulating material providing a recess in which a reciprocable brush 45is mounted in position to contact the strip 43substantially centrallythereof' when the ring 30 is in normal or brakereleased position.Acompression spring 46 encircling a shank 47 on the brush and actingbetween the brush and the end of the brush recess constantly urges thebrush into contact with the strip 43. Thus, the brush is adapted tocontact the strip continuously throughout the range of oscillation ofthe magnet ring 30 in either direction despite any lateral wobbling ofthe flange armature 29 in its rotation. The conductor 41 leading fromthe rheostat may be secured to the vehicle chassis with its remote endextending into and stationarily supported by the junction box 44 forconnection with the brush 45. Thus a simple and flexible connection isprovided between the brake control means and the actuating mechanis onthe vehicle wheel which connection replaces the hea and usuallycomplicated mechanical or hydraulic operating connections now incommonuse on automotive vehicles for transmitting the braking force to theseveral brakes from the common source of braking power.

It should be observed in passin that with the means herein contemplatedor controlcompared to that required to operate a standard brake footpedal, the present control device can be so closely associated with theaccelerator of the vehicle as to materially reduce the time required forthe driver to withdraw his foot from the accelerator pedal and place iton the brake control pedal, thereby materially reducing the timerequired to initiate the application of the brakes.

The force made available by energizing the magnet of the frictionoperator when the vehicle is in motion may be applied with increasedmechanical advantage to either or both of the expanding devices forsetting the brake. The mechanism herein employed for thus augmenting thefrictional force is adapted to actuate the rock shaft 27 in eitherdirection and includes a substantially straight crank arm 48 rigidlyfixed as by keying to the end of the rock shaft which is located outsideof the casing 15. The crank thus being free to oscillate in a verticalplane disposed outside. of the drum and adjacent the ring 30 may be madeof a length substantially equal to the radius of the ring 30 and thusadapted to provide a moment arm of maximum length for the forceavallable at the driven friction element. As a means for operativelyconnecting the driven element to the crank, alink 49 may be employed,said link being pivotally connected at one end to the outer or free endof the crank and at its other end to a stud 50 outside of the casingmember 31. The stud may be anchored in the ring 30 as by threading intoa boss 51 so as to project through an arcuate slot 52 in the member 31,allowance being thereby made for the necessary oscillation of the magnetin either direction. l,

Preferably the length of the link 49 is such as to hold the crank 48 inperpendicular relation with respect to a diameter including the axes ofthe drum and the rock shaft27 when the ring 30 is in normal or -brakereleased position as shown in Fig. 2. Thus the actuating force appliedto the crank'by the driven friction element acts tangentially of thering 30 and in a direct-ion perpendicular to the crank so that itsmoment arm is substantially equal to the radius of the ring regardlessof the direction in which the crank arm is oscillated. The crank arm 48and the cam block on the rock shaft 27 constitute-in effect a bell cranklever which is capable of transmitting the actuating force to the brakeshoes with a mechanical advantage which is equal approximately to thelength of the crank arm 48 divided by the radial distance between theaxis of the rock shaft 27 and the remotest point of contact between theends of the shoes and theexpanding cam block. In the brake shown inFigs. 1 to 3, as designed for a ten-ton road vehicle, this ratio isapproximately 17 to 1 so that with a frictional force of 1000 pounds(which is produced by an attractive force of 4000 pounds between thefriction elements when a current of 4.75 amperes is passed through acoil of 63 turns, as heretofore explained) the brake shoes will beexpanded with a force of approximately 17,000 pounds.

It will be observed that the operating parts of the force-multiplyingconnection between the driven friction element and the brake shoes areso constructed and arranged that the proper degree of mechanicaladvantage is obtained in spite of the fixed structural relation whichexists in the conventional drum type of brake between the axle, thebrake drum, and the enclosing casing therefor. Thus by arranging thecrank arm 49 so that it'extends in a non-radial direction, that is, atan angle to a diameter passing through the axes of the drum and the rockshaft 27, the length of the arm may be substantially greater than thedistance between the axle and the rock shaft 27 and therefore such as toactuate the expanding device with the desired leverage. By directlyassociating the movable parts of the expanding device with the endportions of the brake shoes, they may be so coordinated structurallywit-h the crank' arm that sufficient multiplication of the actuatingforce is obtained through the combined action of the crank and theexpanding device. Furthermore, all of the parts of the force multiplyingconnections are located so remotely from the axle, and their ran es ofmovements in either direction to apply t e brake are such that theiroperation is not interfered with by the usual steerin brake is adaptedto a dirigible wheel, as shown in Figs. 6 and 7..

An inherent characteristic of brakes wherein the actuating force isderived from the momentum' of the vehicle is that further movement ofthe vehicle is required to set the brake following the operation of thedrivers control device. Therefore, in adapting the momentum principle ofoperation to a brake'for a modern automotive vehicle which mustreknuckle when the present a Ill) spond instantaneously to the driverscontrol, a movement of the vehicle corresponding to only a smallfraction of a revolution of the vehicle wheels is allowable foroperating the brakes. This result is accomplished in the presentinstanceby employing a magnet capablepf exerting an attractive force oflarge magnitude; by magnifying the frictional force without unnecessaryloss of motion; and by operating the augmenting mechanism at a point asremote as practicable from the drum axis. With such a large attractiveforce as may be obtained by the present magnet, only a moderatemultiplication of the frictional force produced is necessary in order togive the required expansive force at the brake shoes. The angle throughwhich the magnet ring must move to take up the normal clearance betweenthe shoe coverings and By combining vthese various factors, the angularmovementof the wheel which is required to set' the brake-followingthe'enerization of the magnet is practically negligile', correspondingin the present'instance to a motion of the vehicleof approximatelytwoinches. J

Another advantage of the present forcemultiplying mechanism .is that itsoperating parts have a wide allowable range of movement so that wear onthe shoe coverings is automatically taken up oneach brakeapplicati on.thereby making the brakes practically self adjusting, and eliminatingthe annoyance and expense incident to the maintenance of properadjustment in ordinary manually operable brakes.

In the present arrangement, the outer end ofthe crank 48 projectsslightly beyond the circumference of the drum flange 29 and preferably'is protected byea'casing having aflat enclosing wall 52 and a peripheralflange 53 secured as by bolts against the closure member 31 and anextended portion thereof. This casing completely encloses that portionof the force-multiplying mechanism which is located outside of the drumclosure and is of such size and shape as to allow for proper movement ofthe operating parts and for clearance. V g The attractive force whichmay be roduced with a ring-magnet of the above 0 aracter, especiallywhen it is to be energized from a storage battery or other source ofrelatively smallcapacity, is greatly impaired by the presence ofa'substantial air gap between the magnetic core and armature and variesto a marked degree with slight changes in the width of the gap. Such acondition, were it to exist in a frictionoperator of the presentcharacter, would be particularly disadvantageous in that it wouldprevent sensitive control of the braking action which is a desirablefeature of brake control in automotive braking systems. For example,with an air gap the greater attractive force and therefore the of agiven width between the magnetic elements, a current of such magnitudemight be required to .draw the elements into contact that excessivebraking action would result by greater frictional force produced afterclosure of the magnetic circuit by such, contact. Thus, the reluctanceof the magnetic circuit would be avariable quantity, and the driver ofthe vehicle, not being able to gage the re luctance at any given time,would be unable to so regulate the current flow as to produce theintended deceleration of the vehicle. Various .fa'ctors would tend toaggravate this difficulty in an operator of the present character,because of the normal relative rotation between the magnetic elements.Among these factors is the fact that the brake is subject to the severestrains and constant jarring incident to the use of the brake on anautomotive vehicle. Otherfactors are the inherentlateral relationshipbetween the magnetic friction elements that the magnetic circuit throughthe elements is substantially closed at the time when the magnet becomesenergized to set the brake. This is accomplished in the present instanceby maintaining intimate mechanical contact between said frictionelements at all times, and the means employed for this purpose comprisesthe coiled spring 46 (Fig. 4) which acts through the brush- 4 5 toresiliently urge one side of the magnetic rlng 30 toward the flange 29.Thus the spring acts to maintain the coacting'surfaces of the elementsin mechanical contact, thereby sub stantially closing the magnetic fluxcircuit atone or more points in spite of the inherent wobbling of thedrum flange during rotation. With an initial metallic path of such lowreluctance, a large magnetic flux and therefore a strong magnetic forcewill be developed upon the energization of the winding even with theminimum current which may be supplied by the rheostat control, and anyportions of the magnet ring not then in contact with the flange will bedrawn instantaneously against the flange, thereby completely closing theflux circuits around the entire periphery of the magnet. Thus, grippingengagement of the magent-ic elements will be' eflected by such a smallcurrent in the magnetic winding that the same current will not produceexcessive braking after complete closure of the magnetic circuit by theengagement. .In this way the uncertainty or variation in the actionwhich would result from'a substantial air gap between the elements iseliminated, and the braking action is governed solely by the strength ofthe vehicle over the entire range of current variation by the controlmeans.

Means supplemental to the springs 27 is provided for normally holdingthe parts of the friction operator against movement in either directionby reason of any frictional engagement between the magnetic elements,and for quickly and reliably restoring the parts to brake-releasedposition upon de-energization of the magnetic winding. In the presentinstance, this means comprises a spring 54 of the hairpin type mountedwithin the auxiliary casing on a stud 55 which projects outwardly fromthe member 31. The spring has an end 56 which is held fixed between astationary pin 57 and the flange 53 and another end 58 which is movableand positioned between opposed lugs on a lateral extension 59 integrallyformed on the crank arm 48. Normally, that is when the crank arm is inbrake-released position, the spring is not under stress, but it istensioned by fiexure of the end 58 during oscillation of the crank ineither direction. Then, when the winding is de-energized to release thebrake, the spring'operates to restore the crank and the partsoperatively connected thereto to the normal position shown in Fig.

2. Since the force thus exerted is applied to the crank arm at asubstantial distance from its axis, the force will be ample to overcomethe normal frictional engagement between the magnetic elements and anyadherence of the elements such as that due to residual magnetism.

To provide an auxiliary brake for use as an emergency or parking brake,the rock shaft 28 and the expanding cam thereof may be arranged formanual operation. For this purpose a crank arm 60 is fixed to the shaft28 outside of the casing 15 and connected through mechanism including arod 61 to a hand lever or other operating means located within the reachof the vehicle driver. Thus, the same shoes are adapted to be actuatedeither by the electrically controlled momen tum actuating mechanism orby manual operation. When the electrically controlled brake is appliedto the dirigible wheels of a vehicle, the manual operating means wouldpreferably be omitted.

Referring now to Figs. 6 and 8 which show the brake applied to the frontor dirigible wheel of an automobile, the general arrangement of theparts and their fu nctional relationship are substantially similar tothe construction hereinbefore described. In the latter figures, however,the specific arrangement is designed to accommodate the usual yoke-typesteering. knuckle structure without interfering with the normaloperation thereof or necessitating any change in its structure or itsconventional relationship to the wheel. s

As illustrated in Fig. 6 the vehicle wheel comprises a disk 7 securedupon a flange 8 of the hub 9 mounted on a spindle 10, the hub beingprovided with conventional antifriction bearings. The spindle 10 isintegral with a yoke or steering knuckle 62 of conventional constructionand pivotally supported upon the adjacent end of the stationary axle 63by means of the pivot pin 64. A conventional steering arm 65 isprovided, preferably integral with the spindle yoke or steering knuckle62, and controlled by a drag link 66 pivoted thereon for manualoperation in a well known manner, not shown herein. The disk 7 supportsupon its outer periphery a conventional rim 67 which carries a pneumatictire 68.

The brake drum 12* has a mounting flange 13 secured to the hub flange 8for rotation with the wheel, the open inner end of the drum beingsubstantially closed by an annular disk member 15 rigidly mounted on asuitable flange 16 provided on the spindle portion of the steeringknuckle.

The braking members comprise shoes 19 similar to those previouslydescribed and similarly arranged Within the drum except that the shoesare held against rotation and at the same time mounted for expansiblemovement by being pivotally secured at one adjacent pair of the ends ofthe respective shoes upon pivot studs 69 rigidly mounted on the casing15 and extending through suitable bearings in the adjacent ends of thebrake shoes. I I

A single cam block 26* is positioned between the opposite adjacent endsof the pivoted brake shoes, the cam block being fixed in relation to arock shaft 28 having a suitable bearing support in the stationary casingmember 15. Oscillation of the cam block in either direction effects thespreading of the shoes into frictional braking contact with the drum 12in similar manner to that pre-' viously described, the shoesbeing-resiliently retained in contact with the cam block by a spring 27*oppositely attached to the respective shoes.

It will be here noted that the arrangement of the shoes, together withtheir pivotal supports and expanding cam, is substantially confinedwithin a narrow annular space immediately adjacent to the periphery ofthe drum and affording a large clear space about the axis of the wheelwherein there is ample room for the location and normal operation of thesteering knuckle and the steering arm extending therefrom.

In the present arrangement the armature element 29 of theelectromagnetic brake actuating members is spaced from the inner edge ofthe drum 12 and positioned substantially nearer the edge of the drumnext to the wheel, preferably being integral with the drum structure.The magnet core element 30, carrying a conductor winding-3 andconstructed as previously described, is positioned about the innerportion of the drum. Immediately outward of the peripheral edge of theflange 29 is provided an annular flange 31 integral with or rigidlysecured to the casing 15*, and providing an outer housing for the magnetring 30*,the flange 31 and inner end of the drum 12 forming an annularchamber for .fioating retention of the core member 30 wherein the lattermay move axially to and from its complementary armature member 29.

The magnetizing winding is energized through a conductor 41* associatedwith a brush structure such as is illustrated in Fig. 4, and whichfunctions also to maintain mechanicalcontact at at least one point"between the ring 30 and flange 29*, as previously described herein.

The operating connections between the oscillatory magnet ring 30 and thecam block 26 are similar to that hereinbefore described and comprise astud 50 mounted on the ring 30 and extending through a suitable slot inthe casing 15*, the stud 50 being pivotally connected by the link 49*with the free end of a crank arm 4:8 rigidly secured upon the rock shaft28*. By this means the oscillatory movement of the magnet ring 30effects the operative movement of the cam block 26 and the applicationof the brakes in similar manner and with similar effect to thatpreviously described. The elements of the operator and the brake shoesare maintained in brake released position, when the magnet isdeenergized, by means of the spring 54* positioned and connected aspreviously described.

It willbe noted that the construction disclosed in Figs. 6 to 8 providesa very compact unitary arrangement of the brake members and parts of theoperator which is readily adaptable to mounting upon a dirigible wheelwherein ample space must be provided for the location and operativemovement of the steering knuckle construction common to such wheels andwherein the pivotal axis of the steering knuckle may be maintained inthe close proximity to the plane of rotation of the wheel necessary tothe ease in steering with safe support 'which has been determined byprevious practice.

It will be seen that the adaptability of the elements comprising thepresent invention to arrangement in compact unitary relation in asubstantially annular space about a clear central space defined by thedimensions of the usual steering knuckle structure, is important insecuring the advantages residing in the present invention to four wheelinstallations I of vehicle brakes. It will also be seen that the actualpower for setting the brake is created within the brake unit itself bythe action of the electromagnetic friction device 29, 30*, which derivesforce from the rotating wheel and transmits the force to the brakingmeans, the conductor 41 constitutin the sole connection between theunitary bra e structure and the drivers control pedal or lever, thuseliminating all mechanical levers and linkage for this purpose.

Summarizing the characteristics of our invention, as they will now beunderstood from the foregoing description, our brake has the qualitiesof (first) requiring negligible physical effort by the driver, (second)producing extremely powerful braking action, (third) extremesensitiveness and uniformity in action throughout the entire range ofdegrees of braking action, and (fourth) simple unitary construction andelimination of operating connections between the drivers control deviceand the brake which would require adjustment.

The two first named qualities flow from electrically controlling thebrake and from derivation of power from the motion or momentum of thevehicle to set the brake.

The factors contributing to the third named quality are the characterand construction of the electromagnetic friction device, i. e., themagnet and its armature; the means (in the present embodiment spring 16)for insuring or maintaining a definite or fixed relation between themagnet and its armature at the instant of energization of the magnet soas to provide a substantially invariable air gap (which in the presentinstance is zero at one point at least) and thereby insure an even oruniform flow of magnetic flux at each successive stage of movement ofthe controlling rheostat and avoid sudden or uneven grabbing of thebrake; the construction and arrangement of the parts of theforce-augmenting connection between said friction device and the brakingmeans by which-the brake will be set upon a small fraction of onerotation of the wheel and will be instantly and positively restored tobrake released position.

The quality named fourth above resides in the construction andarrangement of the parts in a compact unit which creates or derives itsown brake setting power upon energization of the magnet and requires noconnection to the drivers control device other than a simple electricalconductor.

Extended rigid tests of brakes constructed in accordance with ourinvention over a long period of time and under all conditions, speedsand emergencies of driving have demonstrated for the present inventionan ease and accuracy of vehicle control and rapidity of deceleration notpossible with any means of braking heretofore known.-

This application is a continuation of our prior application Serial No.156,355, filed December 22, 1926.

We claim as our invention:

1. A vehicle brake comprising, in combination, a. drum arranged torotate with the vehicle wheel to be braked, a pair of brake shoesmounted within said drum, cam means located between adjacent endportions of said shoes for expanding them against the inner peripheralsurface of said drum, a nonrotatable support closing the open end ofsaid drum, a rock shaft journaled in said support and arranged tooperate said cam means, a crank arm on said rock shaft, a peripheralflange carried by said drum disposed in a plane substantiallyperpendicular to the drum axis, a metallic ring mounted opposite saidflange, and an electromagnetic winding in said ring adapted whenenergized to cause frictional gripping engagement of said ring and saidflange, and means operatively connecting said ring and the free end ofsaid crank arm whereby oscillation of said ring will expand said shoes.

2. An electric vehicle brake comprising, in combination, a drum arrangedto rotate with the vehicle wheel to be braked, a non-rotatable membercooperating with said drum to provide a closed casing, brake meanswithin said casing, an electromagnet located within said casing andadapted when energized to engage frictionally with a rotating surface onsaid drum, and a force multiplying connection for transmitting movementof said magnet to said brake means, a portion of said connection beinglocated outside of said casing.

3. An electric vehicle brake of the momentum type, comprising incombination, a drum rotatable with the wheel to be braked, braking meanswithin said drum, expanding means therefor including a rock shaftextending parallel to the drum axis and disposed near the periphery ofthe drum, an electromagnetically controlled friction device having adriving element rotatable with said drum and an oscillatory drivenelement mounted coaxially of the drum, said elements being adapted forfrictional gripping engagement by a force acting in an axial direction,a crank arm fixed to said rockshaft and extending when in brake-releasedposition in a direction substantially perpendicular to a diameterthrough the axes of said drum and rockshaft, and means rigidlyconnecting said driven element to the free end of said crank arm.

4. An electric vehicle brake of the momentum type comprising, incombination, a drum rotatable with the vehicle wheel to be braked, anexpansible braking means within said drum, means carried by said drumand providing an inwardly-facing friction surface, a substantially rigidmetal ring mounted for oscillatory movement and adapted for frictionalgripping engagement with said surface by a force acting axially of saidring, electromagnetic means for causing such engagement, a rockshaftextending through said ring and spaced from the drum axis, means carriedby said rockshaft for expanding said braking means, means operable toapply the actuating force derived through oscillation of said ring ineither direction to said rockshaft including a crank arm fixed to saidrockshaft, and means normally acting to maintain said ring inbrake-released position.

5. An electric vehicle brake of the momentum type comprising, incombination, a drum rotatable with the vehicle wheel to be braked, agripping device engageable therewith, a friction device adapted to beoperated by electromagnetic action whereby to derive an actuating forcefrom the motion of said wheel, mechanism for receiving said force andapplying the same to said gripping device, said mechanism including acrank arm mounted for oscillation in a plane perpendicular to the drumaxis, and means operable upon deenergization of said device afteroscillation of said crank in either direction to apply a force to saidcrank in a direction substantially perpendicular thereto whereby torestore the crank to brake released position.

6. An electric vehicle brake of the momentum type comprising, incombination, a drum mounted on the inner side of the vehicle wheel to bebraked and having an external flange portion providing an inwardlyfacing friction surface, a substantially rigid ring mounted oppositesaid surface for oscillation about the drum axis, an electromagneticwinding adapted when energized to cause magnetic attraction of said ringand said flange, a braking means within said drum, expanding meanstherefor spaced a substantial distance from the drum axis, mechanismreceiving the force resulting from the magnetic attraction andfrictional engagement of said ring and flange and operable to apply suchforce with increased mechanical advantage to said expanding means, andmeans acting to maintain said ring and said mechanism in brake-releasedposition when said winding is deenergized.

7 An electric momentum brake for a vehicle wheel supporting an axlecomprising, in combination, a drum rotatable with said wheel, expansiblebraking means within said drum, a friction device having a drivingelement carried by said drum externally thereof and an annular drivenelement adapted for frictional gripping engagement with said drivingelement by a force acting along the axis of said drum, a non-rotatablecasing arranged concentrically with said axleand supporting said drivenelement in centered position opposite said driving element and foroscillatory movement, mechanism for applying the rotary power derivedthrough the engagement of said elements and to said braking means, andelectromagnetic means by which the degree of frictional engagementbetween said elements may be variably controlled.

8. An electric momentum brake for a ve- .hicle wheel supporting an axlecomprising,

in combination, a drum carried by said wheel with one end thereofadjacent said wheel, braking means within said drum having adj acent endportions disposed near the periphery of the drum, a cam memberpositioned between said end portions and adapted for oscillation aboutan axis parallel to said axle whereby to spread said end portions, acrank arm rigid with said cam and extending in a non-radial directionwith respect to said drum when said cam' is in brake-released position,a pair of annularly arranged friction elements mounted for grippingengagement by the action of a force acting axially of said elements, oneof said elements being carried by said drum so as to rotate therewith,said other element being associated with the free end of said crank armso as to actuate the arm upon oscillation of said driven element ineither direction, and electromagnetic means adapted to be variablyenergized to regulate the degree of frictional pressure between saidelements in setting the brakes.

'9. An electric vehicle brake of the momentum type comprising, incombination, a drum which rotates during motion of the vehicle, abraking device engageable therewith, actuating means for said brakingdevice including a crank arm mounted to oscillate in a path notincluding a diameter of said drum, a pair of friction elements adaptedfor gripping engagement by a force acting in a direction axially of saiddrum, one of said elements bein operatively associated with the free end0 said crank arm so as to actuate the arm upon oscillation in eitherdirection, and electromagnetic means b which the degree of grippingengagement etween said elements may be variably controlled.

10. An electric momentum brake for a vehicle wheel supporting an axle, adrum which rotates with said wheel, a braking device adapted formovement into engagement with said drum and having adjacent endportions, means associated with said end portions and operable to applysaid device to said drum, said means including a crank arm normallyextending in a non-radial direction with respect to said drum axis whenin brake-released position, said arm being mounted to oscillate about afixed axis which is spaced from and extends parallel to said axle, twoannular friction elements adapted for gripping engagement b the actionof a force acting axially of said rum, one of said elements having afriction surface which rotates with said drum, said otherelement beingcon-- nected to the free end of said crank arm so as to a ply thereto anactuating force derived t rough the engagement of said 'elements, andelectromagnetic means b which the degree of gripping en agement etweensaid elements may be variably controlled.

11. An electric momentum brake for awheel supporting a vehicle axlecomprising, in combination, a drum which rotates about said axleduringmotion of said wheel, segmental brake members arranged around said axlewithin said drum, an expanding device spaced from said axle and adaptedto work against adjacent end portions of said members, an outwardlyprojecting substantially radial flange carried by said drum andproviding an annular friction surface of narrow ,radial width whichfaces inwardly relative to said wheel, an annulus of substantially thesame radial width as said surface supported opposite the surface forfrictional engagement therewith, an electromagnetic winding adapted whenenergized to cause attachment of said annulus magnetically to saidsurface, and force-multiplying mechanism connecting said annulus andsaid expanding means.

12. An electric momentum brake for a Wheel supporting a vehicle axle,comprising, in combination, a drum rotatable with said wheel andarranged concentrically about said axle, brake means arranged withinsaid drum about said axle and having adjacent separable end portions,means operable to spread said end portions whereby to expand said brakemeans against said drum, a driving element carried by said drum andhaving a friction surface of narrow radial width and of substantiallythe same diameter as said drum, an oscillatory driven element having andsaid expanding means, and means operable to restore said driven elementand said mechanism to brake-released position after deener ization ofsaid electroma etic means.

13. 11 electric momentum rake for a vehicle having, in combination,friction brake members adapted when engaged to check the motion of saidvehicle, and an actuating mechanism comprising a friction element whichnormally rotates vwhen the vehicle is in motion, an ascillatory frictionelement connected to one of said friction members for operating thesame, an electromagnetic winding associated with one of said elementsand adapted when energized to draw the elements into frictional grippingengagement and thereby cause oscillation of said driven element, and

yieldable means acting on one'of said elements and normally tending tour e said elements resiliently toward each ot er;

14. An electric momentum brake for a vehicle having, in combination,frictionbrake members adapted when engaged to'check the motion of saidvehicle, a friction element which rotates when said'vehicle is inmotion,

a driven friction element adapted for engagement with said rotatingelement and when so engaged to derive an actuating force from themomentum of the vehicle and apply such force to one of said brakemembers, an electrical winding adapted when energized to magnetize saidelements and thereby cause them to be drawn into gripping engagement,and means supplemental to said winding acting to urge said elements intoclose proximity to each other and thereby decrease the reluctance of themagnetic circuit through said elements.

15. An electromagnetic vehicle brake having, in combination, twomagnetic elements mounted for relative rotation, means for magnetizingsaid elements to cause attraction toward each other, and means actingautomatically to urge said elements into close proximity and therebydecrease the reluctance of the magnetic circuit through said elements.

16. An electric momentum brake for a vehicle having, in combination, arevoluble member, a braking device adapted for engagement with saidmember whereby to control the motion of said vehicle, a friction elementwhich normally rotates simultaneously with said member, a secondfriction element adapted for engagement with said first mentionedelement and operatively connected to said braking device for actuatingthe same, an electrical winding associated with one of said elements andforming therewith an electromagnet ofwhicli said other element is the Farmature, and means normally operating to maintain intimate mechanicalcontact be tween 'said elements and thereby provide a substantiallyclosed metallic circuit for the flow of magnetic flux produced upon theinitial energization of said winding.

17. An electromagnetic brake for a vehicle wheel having, in combination,a magnetic element rotatable with said wheel and having an annularfriction surface spaced a substantial distance from the wheel axis anddisposed in a plane substantially perpendicular to said axis, a secondmagnetic element mounted opposite said first mentioned element andhaving a friction surface adapted for coacting engagement with saidother surface, an electromagnetic winding carried by one of saidelements and adapted when energized to cause magnetic attraction whichproduces a force acting in an axial direction thereby causing grippingengagement of said elements, and means supplemental to said windingacting automatically to urge said elements into intimate mechanicalcontact with each other and thereby decrease the reluctance of themagnetic circuit through said elements.

18. An electric vehicle brake of the momentum type comprising, incombination, a drum which rotates during motion of the vehicle, brakingmeans mounted within the drum and having adjacent end portions locatednear the periphery of the drum, means located near and cooperating withsaid end portions for expanding said braking means, a magnetic elementmounted to rotate with said drum and having an annular friction surfacedisposed externally of the drum, a driven magnetic element mounted foroscillatory movement and adapted for frictional engagement with saidannular surface, electromagnetic means adapted when energized tomagnetize said elements and thereby cause gripping engagement thereof,means operative to transmit force from said driven element to saidexpanding means, and means acting to restore said oscillatory frictionelement to brake-released position.

19. An electric vehicle brake of the momentum type comprising, incombination, a drum arranged to be mounted on the inner side of thevehicle wheel to be braked with one end thereof closely adjacent to saidwheel, braking means mounted within the drum and having adjacent endportions located near the periphery of the drum, means located near andcooperating with said end portions for expanding said braking means, anelement mounted to rotate with said drum and having an annular frictionsurface, a driven element mounted for oscillatory movement and adaptedfor frictional gripping engagement with said annular surface,electromagnetic means adapted when energized to produce a force actingin an axial direction thereby causing such engagement, and meansoperative to transmit force from said driven element to said expandingmeans with increased mechanical advantage.

20. An electric vehicle brake of the momentum type comprising, incombination, a drum arranged to be mounted on the inner side of thevehicle wheel to be braked with one end thereof closely adjacent to saidwheel, braking means mounted within the drum and having adjacent endportions located near the periphery of the drum, means located near andcooperating with said end portions for expanding said braking means, anelement mounted to rotate with said drum and having an annular frictionsurface disposed externally of the drum, a driven element mounted foroscillatory movement and adapted for frictional gripping engagement withsaid annular surface, electromagnetic means adapted when energized tocause such engagement, and means operative to transmit force from saiddriven element to said expanding means.

21. An electric vehicle brake of the momentum type comprising, incombination, a drum which rotates during the motion of the vehicle,friction brake means mounted within said drum and having adjacent endportions, a non-rotatable support, a member mounted on said support tooscillate on an axis which extends parallel to and is gagement with saiddrum, two friction elements having opposed surfaces disposed externallyof the axis of said member and adapted to be frictionally grippedtogether one of said elements being carried by sai drum, the otherelement being adapted for oscillation about the drum axis and opera;tively connected to said member for actuating the same, electromagneticmeans adapted when energized to cause frictional engagement of saidelements, control means by which the flow of current in saidelectromagnetic means may be varied in successive increments to regulatethe degree of gripping force between said elements, and means forrestoring the said last mentioned element and said expanding means tobrake-released position when the flow of current in said electromagneticmeans is interrupted.

22. An electric vehicle brake of the momentum type comprising, incombination, a rotatable drum, expansible brake means within said drum,expanding means therefor, actuating mechanism for said expanding meansincluding two friction elements arranged for gripping engagement oneadapted to rotate simultaneously with said drum, the other beingoperatively connected to said expanding means for actuating the same, anelectromagnetic winding adapted when energized to cause grippingengagement between said elements, spring means normally acting tocontract said brake means w1th1n said drum, and supplemental springmeans acting on said mechanism for restoring the mechanism tobrake-released position upon the de-energization of said winding.

23. An electric vehicle brake of the momentum tvpe comprising. incombination, a drum which rotates during motion of the vehicle wheel tobe braked, expansible brake means within said drum, spring means actingto contract said brake means, two magnetic elements adapted to be drawninto frictional gripping engagement upon the energization of anelectromagnetic winding carried by one of said elements. a second springmeans tending to resiliently urge said elements into close proximity toeach other, one of said elements being arranged to rotate simultaneouslywith said drum. said other element being mounted for oscillation whenmagnetically attracted to said rotating element, means connected to saidoscillatory element and adapted to apply the force derive-d through themedium of said elements to said brake means with increased leverage soas to expand the same, and supplemental spring means operable tomaintain said oscillatory element and said force augmenting means inbrakereleased position when said winding is deenergized.

24. An electric vehicle brake of the momentum type comprising, incombination, a brake drum which rotates with the vehicle wheel to bebraked, friction braking means movable into gripping engagement withsaid drum, means operable upon a small fraction of one revolution of thevehicle wheel in either direction for moving said braking means intobraking engagement with said drum, the last mentioned means including anelectro-magnetically operated friction device deriving an actuatingforce from the motion of the vehicle and arranged to transmlt said forceto said brake-applying means, the coacting magnetic elements of saiddevlce being unrestrained from movement toward each other, and meansacting to prevent rotation of the driven element of said device byreason of its frictional engagement with the driving element except whenthe said device is magnetized.

25. An electric vehicle brake of the momentum type comprising, incombination, a member which rotates during motion of the vehicle, arelatively non-rotatable device arranged for braking engagement withsaid member, an annular element composed of magnetic material andnormally rotating simultaneously with said member, a second annularelement mounted for oscillatory movement and arranged for frictionalgripping engagement with said first mentioned element by a force actingin an axial direction, a winding comprising a coiled electricalconductor extending continuously in a series of turns to form an annulusand disposed in a single annular recess in one of said elements, so thatwhen energized said winding will constitute the inner and outer portionsof that element as magnetic poles of opposite polarity, control means bywhich the flow of current in said winding may be varied in successiveincrements to regulate the degree of attractive force between saidelements, means connecting said second element and said brake device andadapted to apply the force derived through the frictional engagement ofsaid elements to said device with increased leverage, and means forrestoring said last mentioned element and said con necting means tobrake-released position when the flow of current in said winding isinterrupted.

26. An electric vehicle brake of the m0- mentum type comprising, incombination, a drum mounted on the vehicle wheel to be braked, frictionmeans within said drum, expanding means therefor, a member cooperatingwith said drum to provide a closed casing, mechanism including a pair ofelectromagnetically operable friction elements adapted to derive anactuating force from the motion of said drum for application to saidexpanding means, an insulated electrical conductor having anon-rotatable mounting on said member and having a connection withinsaid casing to the magnetizing winding for said elements which allowsfor oscillation of the elements.

27. An electric vehicle brake of the momentum type comprising, incombination, a drum carried by the vehicle wheel to be braked brakingmeans adapted for engagement therewith; a driving friction elementcarried by said drum; a driven element adapted for frictional grippingengagement with said driving element; mechanism operable to transmit theangular motion of said driven element to said braking means; anon-rotatable member closing the open end of said drum and supportingsaid braking means, said driven element and said mechanism; anelectromagnetic winding carried by one of said elements and adapted whenenergized to cause frictional engagement of said elements; and meansproviding an energizing circuit for said winding including a contactterminal non-rotatably mounted on said member and having an electricalconnection I with said winding which allows for movement of said windingin the operation of said elements;

28. momentum brake for a vehicle wheel supporting an axle comprising, incombination, a drum mounted on said wheel, braking means adapted formovement into engagement with said drum, a driving friction elementcarried by said drum externally thereof and providing an inwardly facingsurface of relatively narrow radial width and of a diametercorresponding approximately to that of said drum, a substantially rigidmetallic ring constituting a driven element and having a surfacecorresponding in radial width to and adapted for engagement with saidfirst mentioned surface, a relatively stationary support having bearingsurfaces disposed a substantial distance from said axle for supportingsaid ring concentric with said drum for oscillatory movement whenengaged by said driving element, means by which the degree of frictionalpressure between said elements may be varied, and mechanism actuated byoscillation of said ring to apply said braking means to said drum.

29. An electromagnetic momentum brake for a vehicle wheel which supportsan axle having a pivoted yoke-type steering knuckle with a wheel spindlethereon, said brake being composed of a single individual unitcomprising, in combination, a drum fixed to and rotatable with saidwheel; braking means arranged to frictionally engage said drum; anelectromagnetically controlled friction device arranged to derive powerfrom the motion of said wheel; a force-augmenting connection betweensaid device and said braking means; said braking means, friction device,and connection being correlated in a compact unit in an annular spaceoutside of a central space defined by the dimensions of said steeringknuckle; and an electrical conductor leading from a source of power onthe vehicle and connected to said friction device for energizing thelatter to create a force solely within said brake unit itself foroperating said braking means.

30. An electric momentum brake for a vehicle wheel mounted on ayoke-type steering knuckle which is pivoted to swing on an upright axisadjacent the plane of said wheel, said brake comprising, in combination,a drum carried by said wheel on the inner side thereof; braking meansarranged for engagement with said drum; a friction device operable toderive an actuating force from the motion of said wheel including adriving element rotatable with said drum and a driven element engageablefrictionally with the driving element; electromagnetic means associatedwith said elements and adapted when energized to produce a force forcausing engagement of said elements; and a forceaugmenting mechanismconnecting said driven element and said braking means and operable toactuate the latter in the angular movement of said driven element, theconstituent parts of said device and said mechanism being located in andconfined in their extent of movement in setting the brake to a spaceimmediately adj acent to the periphery of said drum while leaving a freeaxial space of such dimensions as to accommodate said steering knucklewhen the latter is positioned in conventional relation to the plane ofsaid wheel.

31. In an electric friction brake for a vehicle, the combination offriction braking members and mechanism ada ted to derive a force fromthe momentum o the vehicle for actuating said braking means comprising amagnetic element mounted on the vehicle to rotate during motion of thelatter and having an annular friction face disposed substantiallyvertically, a second magnetic element mounted for angular movement aboutan axis of said rotatable element and having a frictional faceengageable with said rotatable face, one of said elements being mountedfor floating movement along said axis to permit of yielding engagementbetween the elements and thereby compensate for the inherent lateralwobbling of the rotatable element, an electromagnetic winding on one ofsaid elements adapted when energized to produce a force of magneticattraction between the elements whereby said rotatable element willexert a frictional force on said second element tending to move thelatter away from normal brake-released position, means operable totransmit the actuating force thus derived to said braking means, and aspring acting constantly in a direction generally longitudinally of saidrotational axis to urge said floating element toward the other elementand thereby maintain intimate contact between said faces while saidwinding is deenergized.

32. An electric friction brake having, in combination, a magneticelement having an annular friction surface which rotates during motionof the part whose motion is to be controlled, a second magnetic elementhaving a friction surface adapted for gripping engagement with saidfirst mentioned surface, one of said elements having concentric polesfacing the other element, a winding mounted between said poles andadapted when energized to create a magnetic flux in the magnetic circuitthrough said poles and the opposing element thereby causing grippingengagement of said friction surfaces, and means acting constantly whilesaid winding is deenergized to maintain the reluctance of said magneticcircuit substantially uniform thereby preventing variation of thereluctance by the inherent lateral wobbling of the rotatable element.

33. In an electric friction brake for a vehicle, a pair of rings ofmagnetic material having opposed annular faces, one of said rings beingrotatable during motion of the vehicle, a winding carried by one of saidrings and adapted when energized to create a magnetic flux which threadsthe ferromagnetic circuit through the faces of said rings therebycausingfrictional gripping engagement the magnitude of which determinesthe degree of braking action, control means governing the closure of anenergizing circuit through said winding, and means supplemental to saidwinding acting automatically to insure the existence of mechani calcontact between the engaging portions of said faces coincident with theapplication of current to said winding by said control means whereby theoperation of the brake in response to said control means is unaffectedby the lateral wobbling of said rotatable ring.

34. In an electric friction brake, the combination 'of cooperatingbraking members and mechanism adapted to derive a force from themomentum of the part to be braked for actuating one of said memberscomprising a rotatable magnetic element having an annular friction face,a second magnetic element mounted for some degree of angular movementand having a frictional face engageable with the face of said rotatableele ment, one of said elements being -mounted for floating movement tocompensate for the lateral wobbling of the rotatable element, anelectromagnetic winding on one of said element-s adapted when energizedto produce a force of magnetic attraction between the elements wherebysaid rotatable element will exert a frictional force on the secondelement tending to move the latter angularly away from normalbrake-released position, means operable to transmit the angular movementof the second element to one of said braking members, means constantlyacting to urge said floatin element toward the other element and t erebyyieldably maintain continuous contact between said faces While saidelectromagnet is deenergized, and spring means overcoming the tendencyof said second element to move away from brake-released position as anincident to said continuous contact.

35. In an electrically controlled momentum actuator for a frictionbrake, the combination of two annular magnetic elements having frictionfaces arranged for axial gripping engagement, one of said elements beingmounted to rotate during motion of the part to be braked, the other beinmounted for limited angular movement ut nor mally held under springeffect against such movement and thereby maintained in a normalbrake-released position, a magnetic winding carried by one of saidelements and adapted when energized to produce magnetic attraction ofthe elements whereby said second element overcomes said spring effectand moves through a limited angular distance to actuate the brake, andmeans for maintaining a substantially uniform reluc 'tance of themagnetic circuit through said elements comprising spring means normallyacting when said winding is deenergized to urge the elements togetherand maintain light mechanical contact between their friction faces whichis insufficient to overcome said spring effect tending to hold said sec-0nd element in brake-released position.

In testimony whereof we have hereunto afiixed our signatures.

ARTHUR P. WARNER.

ADDI BENJAMIN CADMAN.

